International aid groups say that hundreds of Syrian children who have fled the war in their country are facing death by starvation at refugee camps in Lebanon.

The U.N. children's agency UNICEF and other agencies said Tuesday that about 10,000 Syrian children under the age of five living in Lebanon are suffering from acute malnutrition, with 1,800 of them at risk of dying and requiring immediate help to survive.

UNICEF's representative in Lebanon, Annamaria Laurini, called malnutrition "a new silent threat among refugees in Lebanon." She said it was linked to poor hygiene, unsafe drinking water, lack of immunizations and improper feeding practices in young children.

Officials say malnutrition first affects the brain, leaving children without any appetite, and that those under five are especially vulnerable.

UNICEF says that nearly 5.5 million children in Syria and neighboring countries are now affected by the fighting that has lasted almost four years.